So called unitized seals are so named because they can be installed as a unit in the annular space between a pair of relatively rotatable members, such as bearing races. Each of a pair of nested, coaxial metal casings is press fit to one bearing race, while enclosed internal rubbing seals provide sealing contact. Most older designs mold the seals directly to the stamped casings. This requires holding the casings in a mold while the elastomer seal lips are injection molded to and around some part or edge of the casing. This molding step is somewhat difficult to control, since the stamped metal casings do not always perfectly match the shape of the mold cavities in which they are held.
A newer type of unitized seal avoids the seal molding step by using sealing disks precut from flat sheets of polytetrafluoroethylene (PTFE) material, which are separately glued or otherwise bonded to the casings. Potentially lower seal torque or friction is possible with PTFE disks, because of the slippery nature of the material.
A problem faced by both types of seals, integrally molded and PTFE disk type, is the running eccentricity that bearing races are subject to, which continually widens and narrows the annular space between the seal casings mounted to them. Running eccentricity continually compresses and relaxes the seal lips. This exacerbates the stress in a seal, especially when the edge of the lip is bent back sharply at the line of sealing contact.
A seal design of the PTFE disk type is shown in co-assigned U.S. Pat. No. 5,201,533. There, two oppositely facing disks of seal material make four separate areas of continual sealing contact, which alternate in orientation. Therefore, despite any running eccentricity, two of the four alternating areas of sealing contact are always increasing their pressure when the other two are decreasing. The seal is manufactured by cutting the two disks, gluing or otherwise securing them to the casings in a radially overlapping fashion, pushing the casings axially together, beyond their ultimate, installation position spacing, and then pulling them back.
There may be circumstances where an elastomer type seal that had the same level of sealing integrity would be useful, provided a method for its manufacture could be devised that still avoided the step of direct molding to the casing. Ideally, such a method would be no more, and preferably less, complicated than the method disclosed in U.S. Pat. No. 5,201,533.